I am not surprised that you were confused, as there was a temporary problem on the Tropicos.com site where using Quercus costaricensis in the name search was not coming up with proper results. I have never seen this happen before, but now it is fixed and does give Q. costaricensis as the accepted name for the species. Encino Negro, or Roble Negro, are also common vernacular names for this species, and are probably better than just Encino, as this name is also commonly applied to Quercus insignis as well. Additionally, it is useful to know that both Encino and Roble are simply two words meaning oak. Any confusion on your part was totally justified and due to peculiar and presumably rare circumstances at the site. There is also always some inevitable confusion related to use of common names, which may be used for a number of unrelated species that have some common characteristic, or occasionally for all members of a genus for example, and Tropicos has very little data on common names, probably because it covers many species that range through several countries, each with a different name for a given tree species. Sorry for rambling.

I am back in the US now till probably sometime in August, but if I am reminded I can ask around about other seed sources when I am back in Costa Rico, or if you send me a private note, I can connect you with a young Costa Rican dendrologist friend who might know.